Can anyone tell me what, generally, are the differences between a GP Ridewatch and an SG Ridewatch? All I can find is that GP "sometimes have less sounds than SG", which doesn't tell me an awful lot.

Functionally the sounds are a bit less clear, and they lack the ability to "change faces." The sounds are typically activated by a button on the back and cycle so that can mess with the noise they make when put in the driver (sounds go: rider name, rider description, driver jingle). Also the candy toy ones lack lights.